Evolutionary stages

T. cruzi undergoes three distinct morphological and physiological evolutionary stages during its cycle, which are identified by the relative position of the kineto- plast in relation to the cell nucleus and the flagellum’s emergence.8 All these evolutive forms can be identified in microscopy in Giemsa-stained preparations (Figs. 16.1-16.3).

Amastigote form of Trypanosoma cruzi in cell culture stained by Giemsa

Figure 16.1 Amastigote form of Trypanosoma cruzi in cell culture stained by Giemsa.1

Epimastigote forms of Trypanosoma cruzi in axenic culture

Figure 16.2 Epimastigote forms of Trypanosoma cruzi in axenic culture.10

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Figure 16.3 Trypomastigote forms of Trypanosoma cruzi from blood stained by Giemsa showing differential morphological aspects,10 according to the Andrade79 classification.

3. Trypomastigotes (Fig. 16.3) present a large free flagellum which originates after the nucleus.9 This stage is the most important, classically known as infective form, and trypomastigotes are present in the blood of mammalian hosts (called blood trypomastigotes), and infect triato- mine vectors during blood sucking. This stage is also present in the feces and urine of the triatomine vectors (called metacyclic trypomastigotes) where it is eliminated during blood feeding onto the skin or mucous of the feeding source. They originate from the epimastigote forms by a process of metacyclogenesis, during the stationary phase of growth in axenic cultures or from amastigotes of cell cultures (Fig. 16.3). These forms do not multiply.

 
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